The solid deposits which are formed inside a pipeline transporting liquid products and/or gases reduce the effective transport cross-sectional area and cause problems to the flow. Such problems are all the more serious when the pipelines carry crude petroleum oil or its related products, particularly when the respective pipelines extend over long distances. If paraffinic crude is to be transported and there is a paraffin wax deposit on the pipe walls, a first approach to solve the problem would be to induce melting of the deposit by localized heating. Nevertheless, it is not an easy job to effect the heating of these pipelines because, in general, such pipelines are very long and the clogged sites are not easily accessible, particularly in the case of submerged or buried pipelines. Therefore, processes were developed to apply in situ heating to cause the melting of meltable deposits (particularly paraffin wax) and their subsequent removal by mechanical means.
GB-A-2276218, hereby incorporated as reference, describes a thermo-chemical dewaxing process of hydrocarbon transmission conduits which comprises applying to the partially clogged pipeline, in the direction of the flow, a water-in-oil emulsion made up of inorganic reagents which are made to react and generate nitrogen gas and heat, the paraffin clog being fluidized and removed by flushing slugs.
EP-A-0642847, also incoporated as reference, relates to a pig designed to be employed in pipelines having meltable paraffin deposits which can be made to melt by providing a foam pig with heat-generating reagents either by impregnating its pores or by placing such reagents inside a cavity of the pig, so that upon reaction the reagents produce a strongly exothermic reaction whereby the displacement of the pig along the pipeline, together with the heat produced by the exothermic reaction, melts the paraffin deposits which are thereby entrained and removed from the pipeline together with the pig.
However, such prior art processes show serious drawbacks related to the scheduling of the start and the duration of the thermo-chemical reactions involved. Inasmuch as such processes are based on the displacement of chemical reagents which, upon reaction or by the effect of certain physical-chemical processes, cause localized heating at critical sites partially clogged by deposits of meltable solids, a certain time period for displacement of the reagents must be allowed before the exothermic reaction begins or ceases to remain active. However, chiefly in the case of subsea or buried pipelines, such scheduling is inaccurate due both to a lack of efficient methods for determining the site where the deposits occur on the walls of the pipelines, as well as to the long extents of such pipelines.
A pointed out above, such inaccuracy is greatly accentuated for long subsea or buried pipelines to which the conventional technique, of measuring the pressure log throughout the pipeline either by attaching pressure sensors to the pipeline or by displacing an instrumentation pig along the pipeline, cannot be applied, since either (i) the attachment of such sensors and the data they provide is rendered impossible, or (ii) such instrumentation pigs are highly sophisticated, expensive and extremely sensitive and delicate so that their use being restricted to pipelines of limited extend and nearly clean condition, otherwise such sophisticated instrumentation can be at least damaged, and more probably become jammed and even destroyed if used within a heavy-clogged pipe.